Gene editing that spreads throughout the body could cure multiple diseases

Imagine if a postal worker, instead of delivering a flyer individually to each house, had to give one to a volunteer on each block, who copied it and distributed it to neighbors. That way the postal worker would get the flyers into dramatically more homes. Biologists hope that a similar approach could improve gene editing in the treatment of all kinds of conditions.

The idea is that each cell in the body that receives the initial supply will make lots of copies of the gene-editing machinery and pass most of them on to its neighbors, amplifying the effect. This means that disease-correcting changes could be made in the DNA of multiple cells.

In tests on mice, Wayne Ngo at the University of California, Berkeley, and his colleagues—including CRISPR gene-editing pioneer Jennifer Doudna—were able to triple the number of liver cells that were edited with this approach.

“Essentially, what we’re doing is we’re giving the first cell that receives our instructions to make a little lipid particle that wraps around.” [the CRISPR machinery] in it, so the first cell becomes a factory that can then send these little packets out to other cells,” says Ngo.

The first approved CRISPR treatment for sickle cell disease involves removing blood stem cells from an individual and editing them outside the body before replacing them. However, this is a personalized treatment and therefore extremely expensive. A number of ongoing trials instead involve directly editing cells in the body with a gene editor that will work for many people.

The big challenge is finding ways to deliver the CRISPR machine to a high enough proportion of specific cells in the body. “We know that to cure sickle cell disease we need to modify about 20 percent [blood] stem cells,” Ngo says. “That 20 percent was very, very hard to hit.

This means that if the initial supply reached only 10 percent blood stem cells, but could be boosted locally to 30 percent, it could mean the difference between success and failure.

To achieve amplification, Ngo turned to a protein that helps shed the virus from cells. Once formed in a cell, these proteins associate with both the cell membrane and each other to form a small vesicle or vesicle that breaks away from one cell and can connect to others.

If these viral proteins are physically linked to the CRISPR gene-editing protein Cas9, then the Cas9 protein—and the RNA that guides it to its target—will be packaged into vesicles and transported to other cells.

To test the idea, the team created a piece of DNA encoding the Cas9 virus proteins. When the DNA was injected under pressure into the livers of mice, it reached only 4 percent of the cells, but 12 percent of the cells were gene-edited overall.

For human treatment, gene editing machines would be delivered in other ways. The injection method has just been used for a proof of principle. “It’s not particularly efficient, but it shows that our system makes a difference,” says Ngo. “Triple amplification is a great place to start. I think some of our current delivery systems are good enough to treat some diseases. More might be better, so we’re actively exploring strategies to achieve that.”

In addition to greater efficacy, the amplified gene edit could also allow the use of lower doses, making the treatment safer.

Biologists have been investigating these approaches with vesicle budding for decades, he says Gaetan Burgio at the Australian National University in Canberra, but Ngo’s team may be the first to demonstrate that it works in animals for gene editing. However, Burgio says the researchers have more work to do to confirm their results. “Proper checks and precautions need to be taken to really prove their claims,” ​​he says.

There are already experimental self-amplifying mRNA vaccines, where mRNAs delivered to cells encode machinery that makes multiple copies of the vaccine mRNA. The goal is to make mRNA vaccines safer and cheaper because lower doses are needed. However, in this case, excess mRNAs remain inside the cells where they are made.

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